Aqueous set initiators for slurry seals

ABSTRACT

Quick-set slurry seals are provided by contacting a mixture of aggregate and bitumen emulsion employing sulfonate or sulfate emulsifiers with a water soluble polyvalent metal set initiator in an aqueous medium at high pH.

Umted States Patent 1151 3,695,152

Graf 1 51 Oct. 3, 1972 54] AQUEOUS SET INITIATORS'FOR 2,488,252 110/1949 Wood ..l06/280 x SLURRY SEALS. 2,760,878 8/1956 Lhony ..106/2692,773,777 12/1956 Alexander eta] ..106/277 x [72] f' 2,861,004 11/1958Sucetti ..l06/277 [7 1 um chevrpn Research p y San 3,128,997 4/1964Young ..106/283 x Franc1sco,Cal1f. 3,206,174 9/1965 Young ..l06/283 X 22F1 d: A .5, 1970 3,243,311 3/1966 Rogers et a1....; ..I06/280 13,513,005 5/1970 Bradshaw etal. ..l06/277 1 P1 61,521 2,587,990 3/1952Gardner et 31......106/277 ux 521 US. (:1. ..94/23,94/25, 106/277,Primary Examiner-Joan Evans 0 2g0 [06/283 7 92 117, 00 Attorney-J. A.Buchanau, J1'., G. F. Magdeburger, C.

117/123,117/168,117/169 Tonkm and Fehnnger 51 1111, c1 ..C09j 3/30, c10055/00, c106 3/00 [58] Field 61 Search ..l06/277-283, 123, 7] ABSTRACT106/269, 308 B, 309; 117/100, 92, 123, 168, Quick set slu i rry sealsare prov1ded by contactmg a 94/20'25 252/3115 259/149 mixture ofaggregate and bitumen emulsion employing 56 R f Cted sulfonate orsulfate emulsifiers with a water soluble 1 e erences I polyvalent metalset initiator in an aqueous medium at UNITED STATES PATENTS high P2,898,223 8/1959 Detrick ..l06/277.

9 Claims, No Drawings AQUEOUS SET INITIATORS FOR SLURRY SEALS BACKGROUNDOF THE INVENTION l Field vOf The Invention Slurry seals are used forsurface repair and maintenance to provide rapid repair of pavements soas to minimize the time for which the pavement is closed to traffic andto prolong the life of existing pavements. Conventional slurry sealmixes cure by dehydration. This requires many hours during which theroadway must be closed to traffic.

Recently slurry seal mixes have been developed which set by chemicalreaction between the .components of the mix. These systems rapidlydevelop strength and will tolerate rolling traffic within an hour ofbeing placed. The reactive nature of this system makes it sensitive tothe chemical composition of the system. These variables need to becarefully controlled to achieve good performance.

The first requirement is the pot life. The slurry seal must be capableof being mixed for a reasonable length of time to provide a relativelyhomogeneous composition when spread on the pavement. Therefore, theemulsion must not break and lose the water during the time in which itis being mixed.

The second requirement is the rate at which the emulsion losessufficient'water to form a structure of substantial strength. It isimportant that the emulsion break rapidly losing a significantproportion of the water and set to a hard cohesive usable structure topermit early opening of the pavement to traffic.

The third requirement which is critical is that upon the breaking of theemulsion, a cohesive structure is set up. It is found that depending onthe conditions, the emulsion may be broken and individual clumps ofasphalt-aggregate formed. The clumps do not adhere to one another and,therefore, do not provide a cohesive structure. Such pavement would havelittle practical use.

2. Description Of The Prior Art Copending application Ser. No. 757,137,filed Sept. 3, 1968, teaches a quick-set slurry seal employing asulfonate emulsifier and an alkaline filler such as Portland cement orhydrated lime. Patents of interest in this area are US. Pat. Nos.3,513,005, 3,206,174, 2,773,777 and 2,488,252.

SUMMARY OF THE INVENTION An improved-method is provided for preparingslurry seal pavement permitting careful control of the rate and natureof the slurry seal set. In relatively rapid order with continuousmixing, an aqueous solution of a multivalent cation at a high pH ismixed with mineral aggregate, an anionic bitumen emulsion is added'tothe wet aggregate and the resulting slurry seal then spread onto thepavement. The emulsion breaks with development of a strong coherentstructure and expulsion of water from the mix. The early development ofstrength provides a pavement which may be used within a short time ofbeing laid.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS In laying pavements of quick-setslurry seals, normal slurry seal equipment can be employed. Thisequipment is described in such patents as US. Pat. Nos.

3,128,997 and 3,206,174. The equipment normally provides means formetering aggregate into a mixing container while moving the aggregatetoward the discharge outlet. Fines are added to the aggregate followedby wetting water and bitumen emulsion. The entire mix is then dischargedinto a slurry seal spreader.

In the present invention aggregate is introduced into the mixingcontainer and then wetted with water at a pH of at least ll. Thehydroxide concentration in the water will usually range from a pH of l1.5 to a concentration of one normal in hydroxide, more usually in thepH range of from about 12 to 13.

A multivalent cation in an aqueous medium is also added to theaggregate. Depending on the particular metal cation employed, the metalcation may be present in the water or may be added as a separatesolution, or may be mixed with the wetting water immediately prior tothe addition to the aggregate. The method chosen depends on thesolubility of the metal cation at the high pH level, and the degree towhich it gregate.

Mixing is continued during the addition and when the mix issubstantially homogeneous, it is spread out onto the pavement andallowed to set. When properly carried out, the emulsion coalesces andthe slurry seal sets rapidly, forming a cohesive structure havingsignificant strength within a short time. The pavement may be used asearly as one-half hour after laying, but will continue to build up itsstrength over a period of one or two days. Normally, the pavement is atleast about 0.2 inch in thickness, does not exceed 0.5 inch, and is moreusually 0.25 to 0.4 inch in thickness.

As already indicated, the laying of a quick-setting slurry seal isparticularly sensitive to a wide variety of conditions and variations inmaterials. Therefore, only the more practical limits will be indicatedas to the conditions and the materials, and suggestions made as to themodifications required with particular systems or where one may beworking under unusual conditions.

Usually, the mixing of all of the components will take from about minuteto 5 minutes, more usually from about 1 minute to about 2 minutes. Thewater containing base (hydroxide) is added to the aggregate. The aqueoushydroxide may contain the multivalent cation or the aqueous solution ofthe multivalent cation may be added shortly thereafter or concomitantwith the bitumen emulsion. Preferably, a portion of the aqueoushydroxide solution is added to prewet the aggregate. The portionmay befrom one-quarter to one-half of the total aqueous hydroxide solutionadded. After the components are added,the mixing may then be carried outfor about l to 5 minutes, more usually from about 1 to 2 minutes. Thewhole operation may be carried out continuously, moving the variousmaterials along as one adds the individual ingredients as appropriate.

The individual ingredients will be considered first, and then theproportions of the various materials invdicated.

The first material to be considered is the aggregate. The aggregate willnormally be a mineral aggregate. The aggregate will have particles of asize in the range of about 4 to passing 200 mesh, US. Standard sieve.Either siliceous or limestone mineral aggregate may be used, such asfine sand, and/or crusher dust, crushed granites, cement slag, ormixtures thereof. The size of the aggregate particles will be within theranges normally specified for slurry seal work. See the AsphaltHandbook, Revised Edition, The Asphalt Institute, College Park,Maryland, September 1960, pp. 21 621 8, for example. Also see p. 60 forparticle size.

With the poorly soluble multivalent metal hydroxides an aqueous solutionof an alkali metal base is added to the aggregate. Alkali metalhydroxides which find use are lithium hydroxide, sodium hydroxide orpotassium hydroxide, preferably sodium hydroxide. The cation is notsignificant as long as it is monovalent and provides a solution at thenecessary pH. The pH of the aqueous solution must be at least 1 1,preferably at least 1 1.5 and preferably in the range of 12 to 13. Thehydroxyl concentration will generally not exceed one normal.

With water soluble multivalent metal hydroxides, the metal hydroxide maybe used, provided that the appropriate concentrations of the metalcation and hydroxide are obtained. Otherwise, the multivalent cationsare added as a separate aqueous solution of an appropriate salt.

Group IIA and llIA metals are employed, having an atomic number of from12 to 56. As a practical matter, only calcium, magnesium, strontium,aluminum or barium will be employed with calcium particularly preferred.The associated anion may be any anion which provides the necessarysolubility. Conveniently, the anion may be halide-particularlychloridenitrate, sulfate, etc. Illustrative salts include calciumchloride, calcium bromide, magnesium chloride, barium acetate, bariumbromate, magnesium formate, magnesium perchlorate, aluminum sulfate,aluminum nitrate, etc.

The remaining component in the mixture is the anionic bitumen emulsion.The emulsion will normally have from about 50 to 70 weight percentpaving bitumen, more usually from about 55 to 65 weight percent pavingbitumen. The bitumen usually employed is asphalt, having a penetrationat 77 F of from about 40 to l 10. The emulsifier will be present in fromabout 0.2 to 2 weight percent, more usually from about 0.4 to about 1weight percent. Other additives may also be present, their amountsvarying from about 0.05 to 3 weight percent. The remainder of theemulsion will be water, varying usually from-about 25 to 49.8 weightpercent.

Included among the other additives which may be present are bentonitewhich may be present in from 0.1 to 1 weight percent and an alkali metalsalt of phenol sulfonic acid, e.g., sodium phenol sulfonate, which maybe present in from about 0.1 to about 0.3 weight percent.

The sulfonate or sulfate emulsifiers will normally be hydrocarbonsulfonates and sulfates. The emulsifiers will usually have molecularweights in the range of about 265 to 450, more usually from about 280 to400. The hydrocarbon groups will be aliphatic, alicyclic oralkyl-substituted aromatics. The hydrocarbon group may have from to 2sites of aliphatic unsaturation.

The preferred sulfonates and sulfates are those having aliphatichydrocarbon groups of from 14 to 30 carbon atoms, particularly preferredis an average of 14 to 20 carbon atoms. Individual sulfonates andsulfates may be used, or mixtures of various hydrocarbon groups havingan average number of carbon atoms or molecular weight within the rangesindicated above. A particularly useful emulsifier is derived by thesulfonation of cracked wax olefins having an average number of carbonatoms in the range of 14 to 20, the individual olefins having from about12 to 28 carbon atoms.

The final composition of the slurry seal prior to being laid and theemulsion broken will now be considered. Arbitrarily, all of the variouscomponents will be considered based on parts of aggregate. All parts areby weight unless indicated otherwise. Usually, from 10 to about 30 partsof emulsion will be employed, more usually from about 15 to 25 parts. Inthe emulsion will be about 5 to 21 parts of bitumen, more usually fromabout 5.5 to 16 parts. The emulsifiers will be present in from about0.02 to 0.6 part, more usually from 0.04 part to 0.3 part. Depending onthe particular emulsifier employed, there usually will be from about0.03 millimole to about 3 millimoles, more usually from about 0.05millimole to about 2.5 millimoles. With the preferred aliphatichydrocarbon sulfonates, the preferred range is 0.12 millimole to about1.0 millimole.

The amount of water added to provide the necessary high pH level and themultivalent cation would normally be from about 5 to 25 parts, moreusually from 10 to 20 parts. The total amount of water present(including the water in the emulsion) will usually be in the range ofabout 7.5 to 40 parts, more usually from about 14 to 32 parts. i

The amount of multivalent cation employed will normally be greater thanabout 0.5 mole and up to about 9 moles per mole of sulfonate or sulfate,more usually from about 2 to 6 moles per mole of sulfonate or sulfateemulsifier. With calcium as the initiator, the calcium will be used inabout 2 to 6 moles per mole of emulsifier. This will be from about 0.01to 0.25 part of Ca per 100 parts of aggregate with preferredcompositions.

The emulsifier employed will generally distribute itself between thesurfaces of the bitumen particles and the aqueous phase in the emulsion.The less emulsifier used, the less emulsifier there will be in theaqueous phase. It is believed that the emulsifier in the aqueous phaseacts to remove the multivalent cation as an effective set initiator.Therefore, the more of the emulsifier that is employed, the more setinitiator that will be required.

In effect, the emulsifier in the aqueous phase serves to stabilize theemulsion against breaking. Therefore, during the mixing, additionalsulfonate can be added, if unusual circumstances are causing too rapid abreak of the emulsion. A too rapid break can occur during the mixing orsubsequent to the mixing when the pavement is being laid resulting inthe slurry seal forming a noncohesive weak structure. It may benecessary when increasing the amount of the emulsifier, all of theconditions remaining the same, to also increase the amount of setinitiator.

In addition, larger amounts of water also tend to retard the developmentof strength in a slurry seal mix. This effect of excess water may becorrected, up to a point, by using larger amounts of the set initiator.It is also found that if the pH exceeds a certain point, 13 or above,particularly with calcium, the setting rate is retarded. However, thiscan vary with other cations. The stability of the slurry seal is alsodependent upon the nature of the aggregate. Limestone tends todestabilize the slurry seal more than silica or siliceous aggregate.Furthermore, the other'variables that tend to stabilize the slurry sealand provide a uniform pavement should also be modified in relationshipto the aggregate employed.

The ambient temperature at which the laying of the slurry seal iscarried out also affects the rate at which the slurry seal sets. Thehigher the temperature, the faster the rate. Therefore, depending uponthe temperature at which the slurry seal is being laid, a more or lessstable slurry seal system will be employed.

ln order to demonstrate the effectiveness of using a liquid setinitiator to enhance the setting of the slurry seal, a number ofexperiments were carried out varying the amount of the multivalentinitiator, particularly calcium, and the amount of base which was addedas sodium hydroxide, to provide the high pH desired. In the followingexperiments, 500 g. of granite dust were mixed with a calcium chloridesolution followed by addition of the caustic solution, the mixture thenmixed, followed by rapid addition of 100 g. of an anionic emulsion. Theanionic emulsion comprises 63 weight percent of an 85/ 100 penetrationasphalt, 0.5 weight percent of bentonite, 0.65 weight percent ofalpha-olefin sulfonate prepared by the sulfonation of cracked waxolefins having from 15 to 18 carbon atoms (see French Patent No.1,419,652), and the remainder water. The following table gives thecompositions employed and the penetration results for a variety of timesafter the slurry seal has been spread.

P-8 Method. The slurry aggregate is poured into a can lid. Consistencyis measured over spaced time intervals using a modified grease cone. Thepenetrometer meets the requirement of ASTM D565. The can lid is 6 indiameter and lk" in height. The temperature is 77F, the lead 400 g. andthe time 5 seconds. The cone is modified by removing the steel tip.

Additional experiments were carried out employing barium chloride andstrontium chloride solutions. Slurry seal mixes were prepared by using500 g. of No. l gradation of Logan Quarry granite dust aggregate, 100 g.of the emulsion previously described and 70 g. of aqueous solution ofstrontium chloride hexahydrate and barium chloride dihydrate at varyingpl-ls. The amount of strontium chloride and barium chloride as theirindicated hydrates are reported in weight percent based on aggregate.With the strontium chloride in from about 0.08 to 0.12 weight percent,excellent slurry seal pavements were obtained in the range from about12.5 to 12.8 pI-l. With the barium chloride in from 0.08 to 0.12 weightpercent, excellent slurry seals were obtained at pl-ls in the range fromabout 12 to 13 with diminishing amounts of barium chloride withincreasing pH.

The next series of tests employed 100 parts of granite dust, 20 parts ofthe previously described bitumen emulsion and a total of 16 parts ofwater containing the calcium chloride dihydrate and the sodiumhydroxide. The calcium chloride and sodium hydroxide were either mixedimmediately before being added to the aggregate or added separately tothe aggregate. The emulsion was then added to the prewet aggregatefollowed by a one-minute mixing cycle. With 0.07 to 0.13 weight percentsodium hydroxide based on aggregate (pH from about 12.5 to 13), thecalcium chloride dihydrate weight percent based on aggregate could bevaried from about 0.2 weight percent to about 0.8 weight percent andrapid setting of the slurry seal to a cohesive structure achieved.

With limestone aggregate in place of the granite, with from about 0.05to 0.3 weight percent sodium hydroxide based on aggregate, the calciumchloride dihydrate amount was varied from 0.2 to 0.8 weight percentbased on aggregate with good results. When the additional water wasreduced to 12 weight percent based on aggregate, and employing a silicaaggregate, the weight percent of sodium hydroxide based on aggregate waspreferably from about 0.05 to 0.2, the amount of sodium hydroxideincreasing with the amount of calcium chloride dihydrate employed whichwas varied from about 0.2 to about 0.8 weight percent based onaggregate.

It is evident from the above results that rapid setting slurry seals canbe obtained by the use of liquid initiators. The advantages of liquidinitiators are manifold. Solutions are much more closely metered thanthe addition of solids, where small amounts of solids are added incomparison to the gross amount of material being employed. Because ofthe liquid nature of the initiator, more complete and intimatedistribution of the initiator with the aggregate and ultimately with theemulsion can be achieved. Greater versatility in the choice ofmultivalent salts is available, particularly where special settingfeatures are required or under unusual circumstances relative to thenature of the aggregate or field conditions. Furthermore, activation ofthe entire aggregate surface is achieved to optimize adhesion of theasphalt to the aggregate. Thus, a longer lasting structurally strongersurface is achieved.

1 claim:

1. A method for laying pavement which comprises:

mixing a mineral aggregate having a mean particle size between about 4and 200 mesh U.S. standard sieve with a solution consisting essentiallyof (1) water, (2) a soluble salt of a multivalent metal selected frommagnesium, calcium, strontium, aluminum, barium or mixtures thereof, and(3) an alkali metal hydroxide in an amount sufficient to impart a pH ofgreater than 11 to said solution, for a period sufiicient tosubstantially wet the surface of said mineral aggregate;

mixing the surface wet aggregate with 10 to 30 parts per 100 parts ofaggregate of an anionic bituminous emulsion having from about 50 toweight percent paving bitumen and from 0.2 to 2 weight percent of a C.,C hydrocarbon sulfate or sulfonate emulsifier to form a pavingcomposition; and

spreading the paving composition onto a surface at a thickness of atleast I/S-inch whereby the mixture rapidly sets into a stable cohesivepavement; said water being present in said paving composition in anamount equal to 5 to 25 parts per 100 parts of said aggregate and saidmultivalent metal being present in an amount of 0.3 to 9 moles per moleof said emulsifier.

2. A method according to claim 1 wherein said multivalent metal iscalcium, the alkali metal hydroxide concentration is in the range of apH of from 12 to 13 and the calcium is present in from 2 to 6 moles permole of emulsifier.

3. The method according to claim 1 wherein said bituminous emulsion hasfrom 0.1 to 1 weight percent of bentonite. v

4. The method according to claim 3 wherein said bituminous emulsion hasfrom 0.1 to 0.3 weight percent of alkali metal phenol sulfonate.

5. The method according to claim 1 wherein said hydrocarbon sulfonateemulsifier is an aliphatic hydrocarbon sulfonate having an average offrom 14 to 30 carbon atoms. 7

6. The method according to claim 5 wherein said emulsifier is derived bythe sulfonation of cracked wax olefins having an average number ofcarbon atoms in the range of 14 to 20.

7. The method according to claim 1 wherein said multivalent metal isbarium or strontium.

8. The method according to claim 1 wherein said mineral aggregate issiliceous, the concentration of alkali metal hydroxide is in the rangeof a pH of 12 to 13, and the multivalent metal is derived from calciumchloride dihydrate which is present in from 0.2 to 0.8 weight percentbased on the aggregate.

9. The method according to claim 1 wherein said aggregate is limestone,the alkali metal hydroxide is derived from sodium hydroxide which ispresent in from 0.5 to 0.3 weight percent based on aggregate and saidmultivalent metal is derived from calcium chloride dihydrate which ispresent in from 0.2 to 0.8 weight percent based on aggregate.

F o v UNITED STATES PATENTOFFICE v CERTIFICATE OF CORRECTION Pat 3, 95,5 I Dated Octobe f 3. 1972 Inventor(s) PETER-E. GRAF It is certifiedthat e rror appears in the abov-identifid patent and that said-LettersPatent are hereby corrected asshown below:

C01. 8, line 19, "0.5" should rea 0105.

Signedjand sealed this ZOth'daY of February 1975.

(SEAL) Attest:

EDWARD MJLETQHERJR. 7 ROBERT GOTTSCHALK Attestlng Offlcer Commissionerof Patents

2. A method according to claim 1 wherein said multivalent metal iscalcium, the alkali metal hydroxide concentration is in the range of apH of from 12 to 13 and the calcium is present in from 2 to 6 moles permole of emulsifier.
 3. The method according to claim 1 wherein saidbituminous emulsion has from 0.1 to 1 weight percent of bentonite. 4.The method according to claim 3 wherein said bituminous emulsion hasfrom 0.1 to 0.3 weight percent of alkali metal phenol sulfonate.
 5. Themethod according to claim 1 wherein said hydrocarbon sulfonateemulsifier is an aliphatic hydrocarbon sulfonate having an average offrom 14 to 30 carbon atoms.
 6. The method according to claim 5 whereinsaid emulsifier is derived by the sulfonation of cracked wax olefinshaving an average number of carbon atoms in the range of 14 to
 20. 7.The method according to claim 1 wherein said multivalent metal is bariumor strontium.
 8. The method according to claim 1 wherein said mineralaggregate is siliceous, the concentration of alkali metal hydroxide isin the range of a pH of 12 to 13, and the multivalent metal is derivedfrom calcium chloride dihydrate which is present in from 0.2 to 0.8weight percent based on the aggregate.
 9. The method according to claim1 wherein said aggregate is limestone, the alkali metal hydroxide isderived from sodium hydroxide which is present in from 0.5 to 0.3 weightpercent based on aggregate and said multivalent metal is derived fromcalcium chloride dihydrate which is present in from 0.2 to 0.8 weightpercent based on aggregate.